Carbon-based composite particle for electron emission device, and method for preparing

ABSTRACT

Disclosed is a carbon-based composite particle for an electron emission source comprising: a particle of a material selected from the group consisting of metals, oxides, and ceramic materials; and a carbon-based material such as a carbon nanotube which is partially buried inside of the particle and which partially protrudes from the surface of the particle.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of Korean Patent Application No.2003-21996 filed on Apr. 8, 2003 in the Korean Intellectual PropertyOffice, the entire disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] (a) Field of the Invention

[0003] The present invention relates to a carbon-based compositeparticle for an electron emission display device and a method forpreparing the same, and, more particularly, to a carbon-based compositeparticle having a high level of electron emission and a method forpreparing the same.

[0004] (b) Description of the Related Art

[0005] Earlier field emission displays (hereinafter referred to as“FED”) were made of a spindt-type electron emission source including Moor Si, with sharp tips of sub-micron size. Since the spindt-typeelectron emission source is assembled with sharp tips of a sub-micronsize, the method of fabricating the same requires a great deal ofattention, and such an operation is considered high-level precisionwork. Therefore, it is difficult and expensive to produce a large-sizedfield emission display device according to this method.

[0006] Carbon material has recently emerged as a potentially usefulelectron emission source due to its low work function. One carbonmaterial, a carbon nanotube (CNT), is particularly expected to be anideal electron emission source since it features a high aspect ratio anda small tip radius of curvature of 100 Å, and thereby electrons arereadily emitted by applying an external voltage of as low as 1˜3 V/μm.

[0007] Generally, the electron emission source is fabricated in such amanner that the carbon nanotubes are formed in a paste with a solvent, aresin, and so on, the paste is applied between substrates by ascreen-printing method, and then it is sintered. Since the carbonnanotubes have a low work function, the resultant electron emissionsource can be driven by applying low voltages, and the method offabricating the same is not complicated. It will thereby offeradvantages for large size panel displays.

[0008] However, when the electron emission source is produced withcarbon nanotubes by the screen-printing method, each carbon nanotube isroughly mixed with a solid powder present in the paste and irregularlydistributed in the solid powder, so that the tips of most of the carbonnanotubes are covered by the solid powder. In addition, most of carbonnanotubes are oriented in a direction parallel with the substrateinstead of the direction perpendicular to the substrate which is wherethe electro-field is applied. Accordingly, the ratio of carbon nanotubesincapable of emitting electrons to all carbon nanotubes is increased sothat the electron emission capabilities are not fully utilized.Generally, an electron emission cathode fabricated by such method has aplanar shape so that the surface area is minimized.

[0009] Therefore, there are considerable demands to find a way to exposethe tips of the carbon nanotubes. As one scheme to satisfy such demands,Korean laid-open patent publication No. 2000-74609 discloses that carbonnanotubes are admixed to metal powders. However, this method requires anadditional process to expose and align the carbon nanotubes, renderingthe process overly complicated. Further, it is difficult to align manycarbon nanotubes perpendicularly, and only a few metal particles havebeen observed to have carbon nanotubes on the surface thereof.

[0010] Further, Japanese laid-open patent publication No. 2000-223004discloses a method for exposing the carbon nanotubes in which carbon andthe metal particulate are mixed and compacted, then the compactedmixture is cut and selectively etched. However, this method is alsoquite complicated and is difficult to apply to a field emission deviceof an electron emission array.

[0011] Moreover, Japanese laid-open patent publication No. 2000-36243discloses a method in which a laser beam is irradiated on the surface ofa printed pattern in which carbon nanotubes are covered with silverparticles combined with a binder, and the silver particles and thebinder present on the surface are selectively removed, so that thecarbon nanotubes are exposed. However, such laser irradiation can tendto thermally damage the carbon nanotubes.

SUMMARY OF THE INVENTION

[0012] According to an embodiment of the present invention, a compositeparticle for electron emission is provided in which many of the electronemission sources are provided in a direction perpendicular to asubstrate.

[0013] In another embodiment of the invention, a method is set forth forpreparing composite particles for electron emission.

[0014] In still another embodiment of the invention, a composition isset forth for forming an emitter of an electron emission display deviceusing the composite particles for the electron emission.

[0015] According to yet another embodiment of the invention, an electronemission display device is provided in which the electron emission isinitiated at low operation power and the electron emissioncharacteristics are improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more complete appreciation of the invention, and many of theattendant advantages thereof, will be readily apparent as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings, wherein:

[0017]FIG. 1 is a schematic view of a composite particle for electronemission according to the present invention;

[0018]FIG. 2 is a process flow chart showing a preparation method for acomposite particle according to one embodiment of the present invention;

[0019]FIG. 3 is a schematic view of a device used for preparing thecomposite particle according to one embodiment of the present invention;

[0020]FIG. 4 is a process flow chart showing a preparation method for acomposite particle according to another embodiment of the presentinvention;

[0021]FIG. 5A is a cross-sectional view of a cathode employingconventional carbon nanotubes;

[0022]FIG. 5B is a cross-sectional view of a cathode employing thecomposite particle of the present invention;

[0023]FIG. 6 is a schematic view showing a process for fabricating acathode according to one embodiment of the present invention;

[0024]FIG. 7 is a graph showing the electron emission of cathodesaccording to Example 4 and Comparative Example 1 at different externalelectric field strengths;

[0025]FIG. 8 is a partial sectional view of a conventional fieldemission display; and

[0026]FIG. 9 is a partial sectional view of another conventional fieldemission display.

DETAILED DESCRIPTION

[0027] The present invention relates to a carbon-based compositeparticle for electron emission comprising a particle selected from thegroup consisting of metals, oxides, ceramic materials, and combinationsthereof; and a carbon-based material which is partially buried inside ofthe particle and which partially protrudes from the surface of theparticle.

[0028] In one embodiment of the invention, a method is provided forpreparing a carbon-based composite particle for electron emissioncomprising: a) dissolving a metal particle precursor in a solvent toobtain a solution; b) adding a carbon-based material to the solution andmixing the solution; c) reducing the metal particle precursor to produceand grow a metal particle, wherein the carbon-based material ispartially buried inside of the metal particle and partially protrudesfrom the surface of the metal particle.

[0029] In yet another embodiment of the invention, an electron emissionsource is provided comprising the carbon-based composite particle.

[0030] In still another embodiment of the invention, a composition isprovided for forming an electron emission emitter comprising thecarbon-based composite particle.

[0031] In still another embodiment of the invention, a field emissiondisplay is provided comprising an electron emission source formed byprint-coating the composition for forming the electron emission emitter.

[0032] Also, the present invention relates to a composite particle foran electron emission source, comprising: a particle comprising amaterial selected from the group consisting of metals, oxides, ceramicmaterials, and combinations thereof; and a material of a cylindricalshape which is partially embedded within the particle and whichpartially protrudes from the surface of the particle.

[0033] Hereinafter, the present invention is described with reference tothe drawings in a more detailed manner.

[0034] As shown FIG. 1, a carbon-based composite particle 1 for electronemission has a structure in which a carbon-based material 3 partiallyprotrudes from the surface of a particle 2. The particle 2 is composedof a material selected from the group consisting of metals, oxides,ceramic materials, and combinations thereof. The particle acts as aneffective supporter for the carbon-based material, and thereby thenumber of emitters for electron emission is increased. In a preferredembodiment of the present invention, the carbon-based materialpreferably occupies at least 30% of the surface area of the compositeparticle, and more preferably between 50 and 90% of the surface area.When the carbon-based material occupies less than 30% of the surfacearea of the composite particle, too few electrons are emitted to ensureintensity.

[0035] The metal, the oxide, or the ceramic material may comprise Ag,Al, Ni, Cu, Zn SiO₂, MgO, TiO₂, and similar materials, and is preferablyAg. The carbon-based material preferably has a cylindrical shape.Examples include carbon nanotubes, diamond, diamond-like carbon,graphite, carbon black, and so on.

[0036] According to the present invention, the carbon-based compositeparticle is one in which the carbon material partially protrudes fromthe surface of the particle, and is partially buried inside of theparticle. Thereby, upon applying the composite particle of the presentinvention to the emitter pattern, the amount of carbon-based materialexposed on the surface and also presented in a direction perpendicularto the substrate is increased so that the carbon-based material canprovide more electronic field effects.

[0037] In addition, since a particle composed of a material selectedfrom the group consisting of metals, oxides, ceramic materials, andcombinations thereof can have a surface roughness on the order of ananometer to a micrometer, the entire surface area accommodating thecarbon-based material is substantially enlarged. This advantageouslyincreases the electron emission effects and the emission currentdensity. In a preferred embodiment of the present invention, theelectron emission source comprising a plurality of the compositeparticles has a surface roughness of at least 10 Å, and preferablybetween 10 Å and 10 μm. In addition, when the composite particlecomprises a metal particle and a carbon-based material, the electricconductivity is improved to reduce the turn-on voltage and the operationvoltage.

[0038] The carbon-based composite particle may be prepared by any one ofa number of methods including co-precipitating, sol-gelling, or thermaldecomposing.

[0039] In order to prepare the composite particle in which thecarbon-based material partially protrudes from the surface of the metalparticle, the co-precipitating method is typically employed. That is,the metal particle precursor (e.g., metal salt) is dissolved in asolvent, and a carbon-based material is dispersed thereto. The metalparticle precursor is reacted in the presence of a catalyst such as areducing agent to produce a metal particle which is then grown. Duringgrowth of the metal particle, the carbon-based material is partiallyburied therein, yet remains partially protruding from the surface,rendering a composite particle of the present invention.

[0040] The type of the metal salt used in the co-precipitating processmay be selected depending upon the metal without specific limitation.However, it is preferably a nitrate or a sulfate.

[0041] According to the method for preparing the composite particles ofthe present invention, the size of the composite particles can beuniformly controlled from several nanometers to several tens ofmicrometers. FIG. 2 shows a process flowchart of the method forpreparing the composite particles. The process comprises a) dispersing asurfactant in a nonpolar solvent to provide a first solution; b)dissolving a metal salt in a nonpolar solvent and dispersing acarbon-based material thereto to provide a second solution; c) mixingthe first solution and the second solution to form a micelle or areverse micelle and adding a reducing agent to produce and grow a metalparticle; and d) heating the micelle or the reverse micelle to removethe nonpolar solvent and the surfactant to provide composite particlesin which the carbon-based material is bound with the metal particles. Inthe method, the particle size is uniformly controlled by forming amicelle or a reverse micelle, to provide uniform photoemission. Further,since the particle size of the composite particle is remarkably reduced,it is possible to provide a display device having a high resolution.

[0042] The size of the composite particles can be controlled byadjusting the concentration ratio of the first solution and the secondsolution. The concentration ratio of the first solution to the secondsolutions is preferably within the range of 1:0.5-30.

[0043] The surfactant preferably has a polar head and a nonpolar tail.Preferred surfactants are cationic, anionic, amphionic, and nonionicsurfactants. The polar head preferably has a nonionic group capable ofhydrogen binding or an ionic group capable of electrostatic binding.Surfactants having ionic groups may include, but are not limited to, oneor more of sulfonates (RSO₃—), sulfates (RSO₄—), carboxylates (RCOO—),phosphates (RPO₄—), ammoniums (R_(x)H_(y)N⁺: where x is 1-3 and y is3-1), quaternary ammoniums (R₄N⁺), betaines (RN⁺(CH₃)₂CH₂COO⁻), andsulfobetaines (RN⁺(CH₃)₂CH₂SO₃ ⁻). In the above compound, R is asaturated or unsaturated hydrocarbon group, and is preferably asaturated or unsaturated hydrocarbon having a carbon number between 2and 1000. Surfactants having nonionic groups may include, but are notlimited to, polyethylene oxides, polypropylene oxides, block copolymersof the form (EO)_(l)(PO)_(m)(EO)_(l) where EO is ethylene oxide and POis propylene oxide, and where l and m are between 1 and 500, aminecompounds, gelatins, polyacrylate-based resins, polyvinylchlorides(PVC), acrylonitrile/butadiene/styrene (ABS) polymers,acrylonitrile/styrene/acryl ester (ASA) polymers, mixtures ofacrylonitrile/styrene/acryl ester (ASA) polymer and propylene carbonate,styrene/acrylonitrile (SAN) copolymers, and methylmethacrylate/acrylonitrile/butadiene/styrene (MABS) polymers.

[0044] The anion bound to the metal ion is preferably removed prior tothe micelle formation. The reducing agent reducing the metal ion to ametal particle may include NaBH₄. The heating temperature for removingthe nonpolar solvent and the surfactant is preferably between 200 and300° C.

[0045] In order to prepare the inorganic composite particle from thesurface of which the carbon-based material protrudes, a sol-gellingprocess is typically employed. A silicon alkoxide such as Si(OCH₃)₄ orSi(OC₂H₅)₄ is subjected to hydrolysis with water using a catalyst suchas hydrochloric or nitric acid and is subjected to polymerization andcondensation reactions, then the metal particle having a desiredparticle size is obtained. When a carbon-based material is added to thereaction, a composite particle can be obtained in which the carbon-basedmaterial is partially embedded within the particle and partiallyprotrudes from the surface thereof.

[0046] If a spray pyrolysis method is used, it can be applied to both acomposite particle having a metal particle and a composite particlehaving an inorganic particle. A detailed description thereof is asfollows, in which spray pyrolysis is carried out by using a device shownin FIG. 3.

[0047] The method comprises a) dispersing a carbon-based material in asolution 10 of a metal particle precursor to provide a dispersedsolution; b) generating a droplet using the dispersed solution; and c)passing the droplet instantaneously through a high temperature tubularreactor 12 using an inert carrier gas, to pyrolize the droplet. As aresult, the particle size of the obtained composite particle can becontrolled to the order of several micrometers and comprises acarbon-based material which is partially embedded in the metal particleor the inorganic particle and which partially protrudes from the surfaceof the particle.

[0048] The precursor solution preferably comprises 0.001 to 10M of themetal particle precursor or the inorganic particle precursor. The metalparticle precursor is preferably a salt of a metal such as Ag, Al, Ni,Cu, or Zn. The inorganic particle precursor may include a siliconalkoxide.

[0049] Further, the concentration of the carbon-based material ispreferably 0.00001 to 100 g/liter. The solvent for forming the precursorsolution may include water or an organic solvent. The organic solvent ispreferably an alcohol such as ethanol, and it may have an acid addedthereto.

[0050] The formation of the droplet 14 is achieved by an ultrasonicsprayer, a nozzle device, or a gaseous sprayer. As shown in FIG. 4, theobtained droplet 4 having a particle size of about 10 to 20 micrometersis shrunk to a solid particle precursor 5 by instantaneous evaporationupon passing through the high-temperature tubular reactor. Theparticular precursor is subsequently pyrolized to generate a compositeparticle in which the carbon based material 3 is partially impregnatedin a needle shape.

[0051] The temperature of the tubular reactor is maintained at between200 and 1000° C., and preferably between 500 and 1000° C. in order tocarry out the evaporation of the droplet and the pyrolysis of theparticular precursor. All components other than the particle materialare completely removed using the gas. It is preferable to introduce ahydrogen gas as a reducing agent together with a carrier gas in order toprotect the carbon-based material from the gas generated upon thepyrolysis. The composite particle generated by being instantaneouslypyrolized in the high temperature tubular reactor is filtered with afilter 16 and collected at the end of the tubular reactor.

[0052] To fabricate an emitter for electron emission from the compositeparticles according to the present invention, a paste is made from amixture of the composite particles, a binder resin, a glass frit, and anorganic solvent. The paste is then printed on a substrate to provide anelectron emission source. The composite particles in the composition arepresent in an amount between 0.01 and 50% by weight, preferably between0.5 and 20% by weight in the composition. The composite particles arepreferably mixed with the glass frit in a ratio of between 5:1 and 1:1.

[0053] The binder resin preferably includes an acrylic resin, anepoxy-based resin, a cellulose-based resin, or similar resins orcombinations of resins, and suitable organic solvents include butylcarbitol acetate (BCA), terpineol (TP), or similar solvents orcombinations of solvents.

[0054] As required, the composition may further comprise aphotosensitive resin and a UV initiator. The viscosity of the pastecomposition is preferable between 5000 and 100,000 cps.

[0055] The paste composition is printed on the substrate and heated toapply to an electron emission source for a display having a desirableshape. The heating process may be carried out in vacuum or under a gasatmosphere. The gas atmosphere may include gases such as N₂gas, or inertgases. Suitable print processes of the electron emission source includespin coating, screen printing, roll coating, and similar processes.

[0056]FIG. 5A shows a cross-sectional view of the conventional cathodefor electron emission formed from the paste composition comprising aconventional carbon-based material, a binder resin, glass frit, and asolvent. As shown in FIG. 5A, the conventional cathode is applied to anemission display constructed from a cathode electrode 20, an insulator22, a gate electrode 24, and a glass frit 26 which is provided to anchorthe carbon-based material. However, little of the carbon-based materialremains on the glass frit 26, while contaminants 28 occupy the most partof the glass frit 26. The contaminants seem to be generated bycombusting the resin of the paste.

[0057]FIG. 5B shows a cross-sectional view of the cathode for electronemission of the present invention. As shown in FIG. 5B, the cathode isapplied to an emission display constructed from a cathode electrode 20,an insulator 22, and a gate electrode 24. In the composite particle 1 ofthe present invention, since the particle 2 acts as a support for thecarbon material 3, a significant amount of carbon material protrudesfrom the particle surface permitting it to effectively emit electrons.

[0058] Since the composite particle according to the present inventionis a conductive material, the electron emission source is obtained byelectrophoresis resulting from an electronic field applied between theelectrode and the patterned substrate. As shown in FIG. 6, the compositeparticle, a solvent, and a surfactant (dispersing agent) are mixed toobtain a dispersed solution. The dispersed solution is then introducedto an ultrasonic container 30 and treated with ultrasound. In theultrasonic container, an electrode plate 32 and a patterned cathodeelectrode 34 are installed with a certain distance from one another, anda bias voltage controlled by the external terminal is applied theretofor a period of time from 1 second to several minutes to deposit thecomposite particles 1 on the cathode electrode. Subsequently, thesubstrate is washed with a solvent and dried to provide an electronemission source. Upon employing the above method, since the heatingprocess is omitted, the electron emission source is more easily preparedcompared to that of a thick film printing process. The surfactant usedin the above method may be the one used in preparing the compositeparticle.

[0059] The following examples illustrate embodiments of the presentinvention in further detail. However, it is understood that the presentinvention is not limited by these examples.

[0060] A field emission display with the inventive cathode isillustrated in FIG. 8. With reference to FIG. 8, gate electrodes 105 arefirst formed on a substrate 103 on which emitters 101 are to be formed.An insulation layer 107 is formed on the gate electrode 105, and cathodeelectrodes 109 are formed on the insulation layer 107. The emitters 101are formed on the cathode electrodes 109. Further, phosphor layers 111are formed on a front substrate 113 on which an anode electrode 115 isformed from a metal material such as Al, for example.

[0061]FIG. 9. illustrates another field emission display with theinventive cathode. As shown in FIG. 9, a cathode electrode 200 is formedon a rear substrate 202, the cathode electrode formed as a plurality ofline patterns. An emitter 204 is provided on the cathode electrode 200.An insulating layer 206 is disposed on the surface of the rear substrate202 to cover the cathode electrode 200 except the emitter 204. A gateelectrode 208 is formed on the insulating layer 206 except over theemitter 204 and has a structure of plural line patterns. Further,phosphor layer 210 and an anode electrode 212 are formed on a frontsubstrate 214 spaced a predetermined distance from the rear substrate202, and having the same structure as the phosphor layer 111 and anodeelectrode 115 of FIG. 8.

EXAMPLE 1

[0062] Preparation of Composite Particles

[0063] 40 g of AgNO₃, 1 g of NH₄OH, 2 g of NaBH₄, and 0.5 g of carbonnanotubes were mixed to generate and grow Ag particles. On growing theAg particles, the carbon nanotubes were partially impregnated in theparticle such that they partially protruded from the surface of theparticles so as to produce composite particles.

EXAMPLE 2

[0064] Preparation of Composite Particles

[0065] 5 wt % polyacrylate resin was dispersed in a nonpolar solvent toobtain a first solution. 5 wt % of carbon nanotubes were dispersed in anonpolar solvent containing AgNO₃ to obtain a second solution. The firstsolution was mixed with the second solution at a ratio of 1:20 toprovide a reverse micelle in which Ag ions and carbon nanotubesco-existed in a certain concentration. A reducing agent was addedthereto and the number of Ag ions were reduced to produce and grow Agparticles. Carbon nanotubes dispersed in the reverse micelle were boundwith the grown Ag particles. The solution comprising the reverse micellewas heated at 200° C. to remove the solvent and the polyacrylate resin.Consequently, Ag-CNT composite particles were obtained.

EXAMPLE 3

[0066] Preparation of Composite Particles

[0067] Carbon nanotube (CNT) powder was dispersed in 0.1 M of an AgNO₃aqueous solution in a concentration of 0.5 g/100 ml to provide asolution. The device shown in FIG. 3 was employed to prepare compositeparticles of Example 3. The resultant solution was agitated to uniformlydisperse the CNT powder, followed by generating droplets using theultrasonic spray device. The generated droplets were introduced into atubular reactor 12 at 400° C. at a flow rate of 1 liter/min using N₂ asa carrier gas. The droplets were instantaneously evaporated in thetubular reactor 12 to be shrunk to solid particles. Thereafter, theparticles were pyrolized to generate Ag particles from AgNO₃, and theremaining components were removed as N₂, NO, or NO₂ gas or vapor, and asCO or CO₂ gas. In order to protect the CNT from the oxygen generatedfrom the vapor or NO_(x) gas, 5% diluted H₂ gas was further introducedas a reducing agent. Ag particles generated by the instantaneouspyrolysis in the tubular reactor were filtered and collected with apaper filter at the end of the tubular reactor to provide Ag-CNTcomposite particles.

EXAMPLE 4

[0068] Preparation of the Electron Emission Source

[0069] The composite particles obtained from Example 1 were mixed withthe glass frit in a ratio of 2.5:1, and was subjected to a ball mill.Then, a vehicle in which ethyl cellulose was dissolved in terpineolsolvent was added thereto and agitated to provide a paste composition.The composite particles in the paste composition were dispersed with a3-roll mill. Then, the composition was screen-printed on the substrateand dried, exposed with a light, and developed to form a pattern. Thiswas followed by sintering at 600° C. to provide an electron emissionsource.

EXAMPLE 5

[0070] Preparation of the Electron Emission Source

[0071] The composite particles obtained from Example 1, a dispersingagent (polyacrylate resin), and pure water were mixed to provide adispersed solution. The obtained dispersed solution was introduced in anultrasonic container 30 as shown in FIG. 6 and subjected to ultrasonictreatment. An electrode plate 32 and a patterned cathode electrode 34were installed at a given distance from one another in the container 30.A bias voltage controlled by the external terminal was applied for 1second to several minutes to deposit the composite particle to thecathode electrode 34. Thereafter, the substrate was washed with purewater and dried to provide an electron emission source.

COMPARATIVE EXAMPLE 1

[0072] Preparation of the Electron Emission Source

[0073] The electron emission source was fabricated by the same method asin Example 4, except that CNTs were used instead of the compositeparticles of Example 1.

[0074] The electron emission sources of Example 4 and ComparativeExample 1 were measured as to electron emission amounts depending uponthe strength of an external electric field, and the results are shown inFIG. 7. It was found that the cathode of Example 4 could initiate theelectron emission at a lower operation voltage compared to that ofComparative Example 1. This is understood to be because the contactingresistance is lowered by the composite particles of Example 1 in whichthe carbon-based material is partially impregnated within the particles.

[0075] Referring again to FIG. 1, for composite particle 1 for theelectron emission source of the display of the present invention, theparticle 2 acts as a support of the carbon-based material 3, so thatmany carbon based materials 3 protrude from the surface of the particle2 to effectively emit electrons. Further, since the circular compositeparticles are provided in a certain area, the surface becomes uneven.The surface area that is capable of accommodating electron emissionsources is thereby increased to increase the emitted current density perunit electric field. Further, the current amount per electron emissionsource is minimized to prolong the life of the display device.

[0076] While the present invention has been described in detail withreference to the preferred embodiments, those skilled in the art willappreciate that various modifications and substitutions can be madethereto without departing from the spirit and scope of the presentinvention as set forth in the appended claims.

What is claimed is:
 1. A carbon-based composite particle for an electronemission source, comprising: a particle comprising a material selectedfrom the group consisting of metals, oxides, ceramic materials, andcombinations thereof; and a carbon-based material which is partiallyembedded within the particle and which partially protrudes from thesurface of the particle.
 2. The carbon-based composite particle for anelectron emission source according to claim 1, wherein the particle isselected from the group consisting of Ag, Al, Ni, Cu, Zn, SiO₂, MgO,TiO₂, and Al₂O₃.
 3. The carbon-based composite particle for an electronemission source according to claim 1, wherein the carbon-based materialis selected from the group consisting of carbon nanotubes, diamond,diamond-like carbon, graphite, and carbon black.
 4. The carbon-basedcomposite particle for an electron emission source according to claim 1,wherein the carbon-based material occupies at least 30% of the entiresurface area of the composite particle
 5. An electron emission sourcecomprising a plurality of carbon-based composite particles according toclaim
 1. 6. The electron emission source according to claim 5, whereinthe electron emission source has a surface roughness of at least 10 Å.7. The electron emission source according to claim 6, wherein theelectron emission source has a surface roughness of between 10 Å and 10μm.
 8. An electron emission source of a field emission display devicecomprising an aggregate of carbon-based composite particles, eachcomprising: a particle comprising a material selected from the groupconsisting of metals, oxides, ceramic materials and combinationsthereof; and a carbon-based material which is partially embedded withinthe particle and which partially protrudes from the surface of theparticle.
 9. The electron emission source according to claim 8, whereinthe particle is selected from the group consisting of Ag, Al, Ni, Cu,Zn, SiO₂, MgO, TiO₂, and Al₂O₃.
 10. The electron emission sourceaccording to claim 8, wherein the carbon-based material is selected fromthe group consisting of carbon nanotubes, diamond, diamond-like carbon,graphite, and carbon black.
 11. The electron emission source accordingto claim 8, wherein the carbon-based material occupies at least 30% ofthe entire surface area of the composite particle.
 12. The electronemission source according to claim 8, wherein the electron emissionsource has a surface roughness of at least 10 Å.
 13. The electronemission source according to claim 8, wherein the electron emissionsource has a surface roughness of between 10 Å and 10 μm.
 14. Acomposite particle for an electron emission source, comprising: aparticle comprising a material selected from the group consisting ofmetals, oxides, ceramic materials, and combinations thereof; and amaterial of a cylindrical shape which is partially embedded within theparticle and which partially protrudes from the surface of the particle.15. The composite particle for an electron emission source according toclaim 14, wherein the particle is selected from the group consisting ofAg, Al, Ni, Cu, Zn, SiO₂, MgO, TiO₂, and Al₂O₃.
 16. The compositeparticle for an electron emission source according to claim 14, whereinthe material of a cylindrical shape is one or more nanotubes.
 17. Thecomposite particle for an electron emission source according to claim14, wherein the material of a cylindrical shape occupies at least 30% ofthe entire surface area of the composite particle
 18. An electronemission source comprising a plurality of the composite particlesaccording to claim
 1. 19. The electron emission source according toclaim 18, wherein the electron emission source has a surface roughnessof at least 10 Å.
 20. The electron emission source according to claim19, wherein the electron emission source has a surface roughness ofbetween 10 Å and 10 μm.
 21. A method of preparing a carbon-basedcomposite particle for an electron emission source, comprising: a)dissolving a metal particle precursor in a solvent to obtain a solution;b) adding a carbon-based material to the solution and mixing thesolution; and c) reducing the metal particle precursor to generate andgrow a metal particle, wherein the carbon-based material is partiallyembedded within the metal particle and partially protrudes from thesurface of the metal particle.
 22. The method of preparing acarbon-based composite particle for an electron emission sourceaccording to claim 21, wherein the metal particle precursor is a metalsalt.
 23. The method of preparing a carbon-based composite particleaccording to claim 22, wherein the metal salt is a salt comprising ametal selected from the group consisting of Ag, Al, Ni, Cu, and Zn. 24.The method of preparing a carbon-based composite particle according toclaim 21, wherein the carbon-based material is selected from the groupconsisting of carbon nanotubes, diamond, diamond-like carbon, graphite,and carbon black.
 25. A method of preparing a carbon-based compositeparticle for an electron emission source comprising: a) dispersing asurfactant in a nonpolar solvent to provide a first solution; b)dispersing a carbon-based material in a nonpolar solvent comprising ametal salt to provide a second solution; c) mixing the first solutionand the second solution to provide a micelle and a reverse micelle andadding a reducing agent to generate and grow a metal particle; and d)heating the micelle or the reverse micelle and removing the nonpolarsolvent and the surfactant.
 26. The method of preparing a carbon-basedcomposite particle according to claim 25, wherein the concentrationratio of the first solution to the second solution is between 0.5 and30.
 27. The method of preparing a carbon-based composite particleaccording to claim 15, wherein the metal salt is a salt comprising ametal selected from the group consisting of Ag, Al, Ni, Cu, and Zn. 28.The method of preparing a carbon-based composite particle according toclaim 25, wherein the carbon-based material is selected from the groupconsisting of carbon nanotubes, diamond, diamond-like carbon, graphite,and carbon black.
 29. A method of preparing a carbon-based compositeparticle comprising: a) dispersing a carbon-based material in a solutionof a metal particle precursor or an inorganic particle precursor toprovide a dispersed solution; b) generating a droplet using thedispersed solution; and c) passing the droplet through a hightemperature tubular reactor using an inert carrier gas to pyrolize thedroplet and form the carbon-based composite particle wherein thecarbon-based material is partially embedded within the inside of themetal particle or the inorganic particle and partially protrudes fromthe surface of the metal particle or the inorganic particle.
 30. Themethod of preparing a carbon-based composite particle according to claim29, wherein the droplet is generated by an ultrasonic sprayer, a nozzledevice, or a gaseous sprayer.
 31. The method of preparing a carbon-basedcomposite particle according to claim 29, wherein the metal particleprecursor is a metal salt.
 32. The method of preparing a carbon-basedcomposite particle according to claim 31, wherein the metal salt isselected from the group consisting of Ag, Al, Ni, Cu, and Zn.
 33. Themethod of preparing a carbon-based composite particle according to claim29, wherein the inorganic particle precursor is a silicon alkoxide. 34.The method of preparing a carbon-based composite particle according toclaim 29, wherein the carbon-based material is selected from the groupconsisting of carbon nanotubes, diamond, diamond-like carbon, graphite,and carbon black.
 35. The method of preparing a carbon-based compositeparticle according to claim 29, wherein the metal particle precursor orthe inorganic particle precursor is present in an amount from 0.001 to10 M in the solution.
 36. A composition for forming an electron emissionemitter comprising a plurality of carbon-based composite particlesaccording to claim
 1. 37. A composition for forming an electron emissionemitter comprising a plurality of carbon-based composite particlesprepared by the method of claim
 21. 38. A field emission display devicecomprising an electron emission source prepared by print-coating thecomposition for forming an electron emission emitter according to claim36.
 39. A field emission display device comprising an electron emissionsource prepared by print-coating the composition for forming an electronemission emitter according to claim
 37. 40. A method of preparing anelectron emission source comprising: introducing a dispersed solutioncomprising a plurality of carbon-based composite particles according toclaim 1, a solvent, and a dispersing agent to an ultrasonic container;and installing an electrode plate and a patterned cathode electrodespaced from one another in the ultrasonic container and applying avoltage thereto to deposit the composite particle on the cathodeelectrode.
 41. A method of preparing an electron emission sourcecomprising: introducing a dispersed solution comprising a plurality ofcarbon-based composite particles prepared by the method of claim 21, asolvent, and a dispersing agent to an ultrasonic container; andinstalling an electrode plate and a patterned cathode electrode spacedfrom one another in the ultrasonic container and applying a voltagethereto to deposit the composite particle on the cathode electrode.